Q switching by saturable absorption in microdroplets: elastic scattering and laser emission

Laser-induced modification of cavity Q's has been achieved in a microdroplet containing a saturable absorber. The elastic-scattering spectra from such droplets for higher incident intensities show that cavity Q's are increased when the absorption is bleached. The lasing spectra from a droplet containing a saturable absorber and laser dye are modified when an intense bleaching field is injected into the droplet cavity after the pump field has initiated the lasing.     

Organophosphorus chemistry. Part 21 [1]. Insertion of olefins into P  CF3 bonds

Tris(trifluoromethyl)phosphine and ethylene reacted efficiently under u.v. irradiation to give 3,3,3-trifluoropropylbis(trifuomothyl) phosphine in good yield. With vinyl fluoride, vinylidene fluoride, and propene the reaction was regioselective rather than regiospecific, and the yield of 1:1 adduct was low. In these reactions, and in those with vinyl chloride, but-1-ene, and hexafluoropropene, in which only traces of 1:1-adduct could be detected, the bulk of the olefin and of the phosphine was recovered, and numerous by-products consistent with radical intermediates were identified. With propyne, 1,1,1-trifluoro-3-bis(trifluoromethyl)phosphino-cis-but-2-ene was obtained in moderate yield, but no reaction occurred between the phosphine and either but-2-yne or hexafluorcbut-2-yne. Tris(trifluoromethyl)phosphine oxide did not form an adduct with ethylene, tetrafluoroethylene, or propyne.Bis(trifluoromethyl)phosphine and dimethylphosphine both reacted readily under u.v. irradiation with 3,3,3-trifluoropropene, the phosphinyl radical attacking the terminal carbon in each case.     

Reactions of 2,2,2-trifluorodiazoethane with carbon-nitrogen and carbon-oxygen multiple bonds

2,2,2-Trifluorodiazoethane reacts with trifluoroacetonitrile in the dark at room temperature to give a 2-(2,2,2-trifluoroethyl)-4, 5-bis(trifluoromethyl)triazole, the 1,2,3-triazole structure being preferred to the 1,2,4-isomer on the basis of the ¹⁹F n.m.r. spectrum. The diazoethane reacts more slowly with trichloroacetonitrile, again forming the N-alkylated triazole even in the presence of an excess of the nitrile. No identifiable adduct resulted with acetonitrile. Hexafluoroisopropyl-ideneimine is first N-alkylated and then undergoes addition to form 1-(2,2,2-trifluoro-1-trifluoromethyl)ethyl-4,5-bis(trifluoromethyl)-?-1,2,3-triazoline, but N-methylhexafluoroisopropylideneimine failed to react. Trifluoroacetaldehyde and trichloroacetaldehyde give mixtures of the ketone (formed by insertion of the CF₃CH group into the aldehyde CH bond) and the $\text{cis}$- and $\text{trans}$-oxirans, apparently $\text{via}$ a β-hydroxydiazoalkane.     

Synthesis of soluble,thermosetting polymides derived from 1,4-phenylenebis(phenylmaleic anhydride) and aromatic diamines

The dianhydride monomer 1,4-phenylenebis(phenylmaleic anhydride) was polymerized with various aromatic diamines in a one-step solution polymerization to afford high molecular weight, soluble polyimides containing backbone phenylmaleimide structures. The polymides were soluble in amide solvents, chlorinated hydrocarbons, and tetrahydrofuran at 25°C at a concentration of 15% (w/v), displayed molecular weight distributions (M_w/M_n) of 2.0–2.2 as determined by absolute GPC and showed T_g values of 240°C and above as measured by differential scanning calorimetry. In addition, polyimide thermosets were prepared from these materials by thermal cure at 350–360°C. The crosslinked polyimides displayed T_gs 20–25°C higher than their soluble precursors, and chloroform extraction indicated gel fractions ranging from 74–100% after cure. © 1994 John Wiley & Sons, Inc.     

Continuum source-atomic absorption spectrometry using a two-dimensional charge coupled device

A single element continuum source-atomic absorption spectrometer (CS-AAS) using a two-dimensional charge coupled array detector (2D-CCD) was assembled for use with graphite furnace atomization. The two-dimensional CCD was a split-frame transfer array, was thinned and back-illuminated for high quantum efficiency at approximately 200 nm, and was capable of an 80-Hz frame rate with a read noise of <15 electrons. The transfer of charges from the integrating arrays to the storage arrays took 0.65 ms, less than 4% of the frame period (16.42 ms). The transfer of charges to the storage array was perpendicular to the wavelength axis, eliminating source flicker noise, and was implemented without masking, producing vertical smearing. The smearing was manifested as a continuum background and was corrected using pixels between orders. The two-dimensional array, in conjunction with the high-resolution echelle spectrometer, allowed measurement of absorbance with respect to wavelength and height in the furnace. Computed absorbances were corrected for stray radiation and non-specific background absorption. Detection limits were equal to those for line source AAS, with the exception of As (193.7 nm) and Se (196.0 nm).     

Photon transitions in Upsilon(2S) and Upsilon(3S) decays

We have studied the inclusive photon spectra in Upsilon(2S) and Upsilon(3S) decays using a large statistics data sample obtained with the CLEO III detector. We present the most precise measurements of electric dipole (E1) photon transition rates and photon energies for Upsilon(2S) --> gammachi(bJ)(1P) and Upsilon(3S) --> gammachi(bJ)(2P) (J = 0, 1, 2). We measure the rate for a rare E1 transition Upsilon(3S) --> gammachi(b0)(1P) for the first time. We also set upper limits on the rates for the hindered magnetic dipole (M1) transitions to the eta(b)(1S) and eta(b)(2S) states.     

Overcrowded molecules. V. 3,10-dimethyl-1,12-bis(2-pyridyl)benzo[c] phenanthrene-2,11-diol

The bis ketene acetal adduct of 4a,10a-diazoniaanthra[1,2-α]anthracene diperchlorate ( 10 ) was used to prepare the highly overcrowded benzo[c]phenanthrene 2 by a known procedure. Its oxidation with cupric chloride provided the isoxazolium zwitterion, 3 , via an intramolecular cyclization.     

Model for predicting the composition of copolyesters: Polymerization of terephthalic acid, 2,2′-oxydiethanol,and 2,2-dimethyl-1,3-propanediol

Copolyesters of two glycols and a dicarboxylic acid moiety are frequently made to obtain specific physical properties. In the synthesis of these polymers an excess of glycol is used in the ester-exchange reaction and then removed during the polycondensation reaction to form a high-molecular-weight product. A model has been developed to predict the final polymer composition. The derivation is based on equilibria of reaction species (free glycol, polymer chain ends, and ester links) and the relative vapor pressures of the two reacting glycols. Calculated results are compared with experimental results of poly(2,2′-oxydiethylene: 2,2-dimethyl-1,3-propylene terephthalate)s. There is good agreement between calculated and experimental compositions. The model can be used to calculate the glycol concentrations that must be used to make a specific polymer composition. This model should also be useful in the calculation of other mole ratios of glycol to dicarboxylic acid that will make the same composition.